According to the telecommunication statistics, the majority of wireless communication traffic occurs indoors, while only a small percentage occurs outdoors or during travelling at high speed. The telecommunication service providers need to find an effective way to balance the two conditions when deploying macrocell stations. The emergence of femtocells solves these problems. A femtocell is a family type station, allowing only a few cell phones to access. Because a femtocell is a low power transmitter, with coverage area of about 30-70 square meters, the femtocell may reduce the resistance faced by the telecommunication service providers during deployment. The deployment of a large number of femtocells may enhance the wireless signal quality in indoor environments, and improve the frequency utilization efficiency. Because of low cost in deployment and management, using a femtocell is becoming a popular solution adopted by the telecommunication service providers.
As the femtocell is the station for indoor use, the authorization and authentication issues are incurred. The closed femtocell allows only the family members or authorized cell phones to access and to obtain services. Because of the authorization issues of the closed femtocell, the non-family-members or non-authorized cell phones may only access the large-area macrocells and a small number of open femtocells. When the on-authorized cell phones roam to a closed femtocell, the access process between the cell phones and the macrocells will interfere with the area of the closed femtocell. On the other hand, the attempt of the femtocell to improve the signal quality will interfere with the access connection between the cell phones and the macrocells. FIG. 1 shows two scenarios of mutual interference between a macrocell and femtocells.
In FIG. 1, macrocell 150 covers the area that includes two closed femtocells 110, 120, with two non-authorized cell phones 111, 121 and two authorized cell phones 115, 125. Cell phones 111, 121 roam into coverage areas 113, 123 of femtocells 110, 120 respectively. Because cell phone 111 cannot access femtocell 110, cell phone 111 may only access coverage area 151 of macrocell 150. When cell phone 111 needs to uplink a large amount of data to macrocell 150, the uplink period will severely interfere with the signal quality of cell phone 115 accessing femtocell 110. This is called uplink interference, and uplink interference degrades the service quality of femtocell 110.
The other scenario is that when femtocell 120 needs to transmit a large amount of information to authorized cell phone 125, the transmission will also interfere with the signal quality of non-authorized cell phone 121 receiving from macrocell 150. This is called downlink interference. When the mutual interferences between two closed femtocells 110, 120 occur, the interference storms are formed.
The current standards and known mechanisms require manual configuration to operate the closed femtocell and set the acceptable International Mobile Subscriber Identity (IMSI)/Mobile Station International Subscriber Directory Number (MSISDN). The femtocells do not include a self-aware and dynamic authorization mechanism to solve the interference situations.